/Engine/Source/Runtime/Core/Public/IO/IoDispatcher.h
Reads and decrypts if necessary the compressed blocks, but doesnotdecompress them. The totality of the data is stored in FIoStoreCompressedReadResult::FIoBuffer as a contiguous buffer, however each block is padded during encryption, so either useFIoStoreCompressedBlockInfo::AlignedSizeto advance through the buffer, or useFIoStoreCompressedBlockInfo::OffsetInBufferdirectly.
[TIoStatusOr](API\Runtime\Core\IO\TIoStatusOr)< [FIoStoreCompressedReadResult](API\Runtime\Core\IO\FIoStoreCompressedReadResult) > ReadCompressed ( const [FIoChunkId](API\Runtime\Core\IO\FIoChunkId) & Chunk, const [FIoReadOptions](API\Runtime\Core\IO\FIoReadOptions) & Options, bool bDecrypt ) const